The Bath Spa MA in creative writing must be doing something right. The course has produced Costa winner Nathan Filer and Samantha Harvey, author of the acclaimed novels The Wildernessand All is Song. Both writers offer glowing jacket puffs to Jason Hewitt, now set to join the list of distinguished alumni with his debut novel, The Dynamite Room.

The novel begins in the blistering summer of 1940, as we meet Lydia, 11 years old, travelling by train and then foot to her home in Suffolk, mysteriously alone. She appears to be running away from something, but more intriguing still is what she discovers in her village: it is eerily empty, and all familiar people and things are somehow missing. The wartime atmosphere of sandbags green with mildew in the abandoned village makes a powerful opening impression, and Lydia is immediately established as an independent and strong-willed girl, refusing a lift from the only person she meets on her journey. She is determined to return to her home, Greyfriars, and reunite with her mother. She even has the courage to face her worst fears: "Maybe it had happened. She had heard people talking about it. She had heard the warnings on the BBC Home Service." She forces herself to put on her gas mask, fearing "they'd let something lose from a plane flying high above them". But she soon abandons the mask and we learn that she has a good instinct both for survival and for sussing out baloney.

So when Lydia discovers not her longed-for family but a stranger with a gun and a German accent, we are not surprised that after her initial shock she doesn't try to escape but stands her ground, thus beginning a five-day standoff inside Greyfriars. The German soldier – Heiden – establishes some ground rules. He won't kill Lydia, but she can't leave. And he has worse news. He is just the first; the Germans have landed on the East Anglian coast and Britain is already in the grip of a German invasion. His colleagues will join him soon. This explains why Lydia found the village deserted, and as corroboration she catches a snippet of the terrifying news on the radio, before Heiden prevents her from hearing more by destroying the wireless with a kick. But is everything as he says it is? And how is it that he already knows her name, when she is sure she didn't tell him?

The relationship between these two characters has echoes of the condition later identified as Stockholm syndrome, as, little by little, Lydia becomes increasingly fascinated by Heiden. Her impact on him is equally significant. Inside the trapped, stifling atmosphere of the house, the story unfolds of how Heiden, once a promising musician, became corrupted by his participation in the war. In an early scene with his young girlfriend Eva he expresses no surprise when she mourns the ejecting of Jewish performers from the orchestra. "He closed his eyes for a moment, shutting her away", and this refusing to "see" evil soon becomes even more significant. Can his passivity in watching – perhaps even participating in – a gang-rape and the shooting of three children be redeemed by later acts of mercy?

With its unshowy, confident prose, this novel is accomplished, resonant and surprising, and poses some delicately handled questions about whether redemption is possible, and at what point a good heart becomes forever besmirched.